The present invention relates to compositions comprising blends of resins. More particularly it relates to blends of aromatic polycarbonate resins and graft derivatives of ethylene-propylene-diene terpolymers which contain an amount of an impact modifying compound effective to positively upgrade the impact properties of said blends and to improve the resistance of said blends to organic solvents.
The aromatic polycarbonate resins are well known in the art and, due to their many advantageous properties, are used as thermoplastic engineering materials. The polycarbonates exhibit, for example, good impact strength and good heat resistance.
Polycarbonate resins have been blended with other thermoplastic materials such as high molecular weight polymeric glycol esters of terephthalic and/or isophthalic acid; and acrylonitrilebutadiene-styrene terpolymers (ABS). Mixtures of polycarbonates with ABS graft copolymers are disclosed to have improved impact properties in U.S. Pat. No. 4,172,103. However, it is disclosed in U.S. Pat. Nos. 3,130,177 and 3,852,393 that impact resistance of polycarbonate resins tends to be lowered by blending them with ABS resins.
The blending art, particularly when dealing with polycarbonates, is thus generally a complex and somewhat unpredictable area where the empirical approach is still generally the rule rather than the exception. Thus, in order to provide a useful binary blend of a polycarbonate with other resins the two resins must be compatible, they must be combinable over certain useful concentrations, and the blend should exhibit a combination of the various advantageous properties of the resins rather than the individual properties of the neat resins. The formulation of blends containing three or more different resins is fraught with a much higher degree of complexity and unpredictability.
Grafted derivatives of ethylene-propylene-diene terpolymers and compositions of such polymers with other resins are known in the art and described in the patent literature. It has been disclosed, for example, that olefinic copolymers and terpolymers can be grafted with styrene, styrene-acrylonitrile, methyl methacrylate, styrene-methyl methacrylate, and the like, to provide thermoplastics which can be further blended, e.g., with styrene-acrylonitrile, and molded, extruded or vacuum formed into articles having good tensile and impact strengths. Polymers of this type and methods for their preparation are described in U.S. Pat. Nos. 4,202,948 and 4,166,081, the former being incorporated by reference. Thermoplastic resin blends of polysulfone resins and graft derivatives of ethylene-propylene terpolymers are disclosed in U.S. Pat. No. 3,641,207 to have good processability and impact resistance over relatively narrow concentration ranges.
Aromatic polycarbonate resins and derivatives of ethylene-propylene-diene terpolymers are combinable with each other over a wide range of concentrations and provide compositions which exhibit advantageous properties after molding. Such properties are obtainable over a wide range of compositions. Especially noteworthy properties are high gloss on the surface of articles molded from these compositions and improved resistance to environmental stress crazing and cracking as compared to aromatic polycarbonate resins. Environmental stress crazing and cracking refer to the type of failure which is hastened by the presence of organic solvents such as, for example, gasoline, acetone, heptane and carbon tetrachloride when such solvents are in contact with stressed parts fabricated from aromatic polycarbonate resins. The most siginificant effect is a loss in the impact strength and an increase in brittle type failure.
While these blends of polycarbonates and graft derivatives of ethylene-propylene-diene terpolymers are useful in a wide variety of applications there exist certain situations which require greater impact strength and better resistance to environmental stress crazing and cracking than possessed by these blends. It is, therefore, an object of the instant invention to provide polycarbonate/graft derivatives of ethylene-propylene-diene terpolymer compositions exhibiting improved impact properties and improved resistance to organic solvents.